1. Field of the Invention
The present invention relates to an ink jet printing apparatus having a suction recovery unit for eliminating an ejection defect of a printing head.
2. Description of the Prior Art
In a conventional ink jet printing apparatus, ink will often not be ejected due to a change in temperature or an impact on the printing apparatus in the normal use. In this case, a bubble at the nozzle tip or an ink of a high viscosity at the nozzle tip is slightly drawn by a suction recovery unit having a small maximum suction capacity, thereby recovering ejection capability. Furthermore, in an abnormal state wherein the printing apparatus is left at a high temperature of about 60.degree. C. for a week or more, the viscosity of the ink is increased, and the ink tank and ink supply tube or the like are substantially filled with air. In the case of recovering the recording apparatus in the abnormal state described above, a plurality of operations must be performed with the suction recovery unit having such a small maximum suction capacity. In order to remove the highly viscous ink by one suction operation, it is proposed that the maximum suction capacity of the suction recovery unit is increased. However, when the bubble is formed at the nozzle tip or when the ink having a high viscosity is left only at the nozzle tip, ink is excessively drawn, resulting in an economical disadvantage.
When an initial space of the cylinder of a piston type suction recovery unit is very small, the negative suction force acting on the ink is excessively increased. Therefore, air dissolved in the ink becomes a bubble which floats around the nozzle and the filter, thereby resulting in ejection difficulties.
Even if the initial space of the cylinder is increased, the drawn ink is replaced with air in the initial space of the cylinder. As a result, the initial space becomes substantially small, thereby increasing the negative suction force of the ink and forming a bubble in the ink jet printing head.